The present invention relates to a system for storage and transportation of an agricultural chemical. More particularly, it relates to an article of manufacture useful in warehousing and shipping of the herbicide glyphosate.
The agricultural industry presents numerous logistical problems to the supplier of goods consumed in that industry, these problems being unique to agriculture or at least more acute than in most other industries. Individual production units in the agricultural industry (such units are called xe2x80x9cfarmsxe2x80x9d herein regardless of whether they fit the traditional image of farms) are more numerous and more geographically dispersed than in any other industry and, even in highly developed countries such as those of North America and Western Europe, are often relatively remote from major transport arteries. For these reasons, transportation costs, both inward and outward, are a significant burden on the industry and improvements in efficiency of transportation are continually sought in order to reduce these costs.
Distribution channels for goods required by the agricultural industry have evolved to deal with the geographical dispersion and large number of farms. In some cases, goods are shipped directly from the point of production to individual farms, but this is rare and is economically feasible only for the largest farms. Generally there is at least one, often more than one, step in the distribution channel between the original supplier and the farm gate. For example, the manufacturer of a good destined for use on a farm supplies a wholesale distribution company, which supplies a retailer or farm cooperative, which in turn supplies the individual farm. Distributors, retailers and cooperatives therefore maintain inventories of such goods, incurring warehousing costs that add to the cost ultimately borne by the farm operation. Improvements in efficiency of storage are therefore also sought, again in order to reduce costs.
Where the good in question is a pesticide, for example a herbicide, the benefits obtainable from improved efficiency of transportation and storage are particularly great. Pesticide products must generally be transported and stored in containers that are more expensive per unit of capacity than those used for many other products such as seeds and fertilizers. Expensive containers are used because of the great importance of container integrity arising from the high price/volume ratio of most pesticides and the fact that many pesticides are potentially hazardous if spilled or leaked.
Typically, therefore, pesticides are stored and transported in as concentrated or compact a form as possible without sacrificing ease of handling by the end-user, who has in most cases to dilute the pesticides in water or another carrier before applying the pesticides to crops, weeds or soil. The larger the amount of pesticidal active ingredient that can be accommodated in a container of given capacity, the lower are the costs of transportation and storage per unit of active ingredient and per unit area of land ultimately to be treated with that active ingredient. That the present state of the art sets an upper limit on the efficiency of packing of pesticides in containers for storage and shipping is well illustrated in the case of the herbicide glyphosate (N-phosphonomethylglycine).
Glyphosate is xe2x80x9cthe largest selling agrochemical in the global marketxe2x80x9d with an estimated annual production of 93,420-114,180 tonnes (Wood Mackenzie Agrochemical Service, Agrochemicals Product Database, 1998). It finds uses for control of unwanted vegetation in virtually every agricultural production system, as well as in forestry, industrial, municipal, residential, rights-of-way, amenity and other applications. Glyphosate is an acid that is relatively insoluble in water (1.16% by weight at 25xc2x0 C.). For this reason it is typically formulated as a water-soluble salt in aqueous solution.
Monobasic, dibasic and tribasic salts of glyphosate can be made. However, it is generally preferred to formulate glyphosate and apply glyphosate to plants in the form of a monobasic salt. The most widely used salt of glyphosate is the mono(isopropylammonium), often abbreviated to IPA, salt. Commercial herbicides of Monsanto Company having the IPA salt of glyphosate as active ingredient include Roundup(copyright), Roundup(copyright) Ultra, Roundup(copyright) Xtra and Rodeo(copyright) herbicides. All such commercial products take the form of concentrated aqueous solutions of glyphosate IPA salt, in most cases together with inert formulation ingredients, principally surfactants. Other glyphosate salts which have been commercially formulated as concentrated aqueous solutions include the mono(trimethylsulfonium), often abbreviated to TMS, salt, used for example in Touchdown(copyright) herbicide of Zeneca.
The great diversity of global markets for glyphosate herbicides has led to a corresponding diversity of container types and sizes, and to a number of more complex storage and shipping systems, for concentrated liquid aqueous formulations of glyphosate salts. Containers used for storing and shipping such formulations are typically constructed of a durable plastic such as high density polyethylene (HDPE), although large bulk tanks are often constructed of other materials such as stainless steel.
Small containers, ranging in capacity from about 0.1 liter to about 10 liters, including the standard 2.5 gallon (9.46 liter) containers widely used in the United States, typically take the form of jugs or flasks with a replaceable screw-cap. They are generally designed for single use and are typically not returned to the supplier when empty, instead being disposed of by the end-user in accordance with local agricultural chemical container disposal guidelines, procedures, regulations or laws. Commonly, a plurality of these small containers are packaged within a single box and a plurality of such boxes are shipped on a pallet. During shipment, the small containers (usually within boxes on pallets) can be disposed in an enclosed volume such as provided by a rail boxcar or road truck, the hold of a ship or aircraft, or a modular box container adapted for transport by road, rail and water.
Larger single-use containers, ranging in capacity up to about 200 liters, for example about 50 to about 200 liters, are commonly in the form of drums, and can be shipped in an enclosed volume as described above, one or more per pallet or unpalleted.
Increasing volumes of liquid aqueous glyphosate products are being purchased by end-users in a large refillable container sometimes known as a shuttle, which typically has an integral pump or connector for an external pump to permit transfer of liquid. Shuttles have a capacity of about 200 to about 2000 liters and are commonly shipped on a pallet.
Liquid aqueous glyphosate products are also shipped in bulk, in large tanks having a capacity of up to about 100,000 liters. The liquid is commonly transferred by pumping to a storage tank at a facility operated by a wholesaler, retailer or cooperative, from which it can be further transferred to shuttles or smaller containers for onward distribution. Bulk shipment is also used for concentrated glyphosate salt solutions to be used as a raw material for preparation of formulated herbicidal products contining additional ingredients such as a surfactant.
A modular bulk shipping tank adapted for road, rail and water transportation typically has a capacity of about 15,000 to about 20,000 liters. A tank truck for road transportation typically has a capacity of about 20,000 to about 25,000 liters. A railcar tank typically has a capacity of about 75,000 to about 90,000 liters.
It will be clear from the storage and shipping containers illustratively described above that all have a limited capacity. Furthermore, when containers are shipped or stored in an enclosed volume, that enclosed volume also has a limited capacity.
Storage and shipping costs for most modes of transportation are primarily related to volume, therefore a system that would permit more compact packing of glyphosate into the available volume or capacity would significantly reduce such costs per unit of glyphosate stored or shipped. Other advantages of such a system would include the convenience and cost saving to the end-user of having fewer containers for disposal, and the resulting environmental benefits; reduced frequency of refilling of shuttles or storage tanks; and further advantages that will be apparent from the disclosure herein.
Various salts of glyphosate, methods for preparing salts of glyphosate, formulations of glyphosate or its salts and methods of use of glyphosate or its salts for killing and controlling weeds and other plants are disclosed in U.S. Pat. No. 4,507,250 to Bakel, U.S. Pat. No. 4,481,026 to Prisbylla, U.S. Pat. No. 4,405,531 to Franz, U.S. Pat. No. 4,315,765 to Large, U.S. Pat. No. 4,140,513 to Prill, U.S. Pat. No. 3,977,860 to Franz, U.S. Pat. No. 3,853,530 to Franz, and U.S. Pat. No. 3,799,758 to Franz. The aforementioned patents are incorporated herein in their entirety by reference.
The highest concentration at which glyphosate IPA salt can conveniently be stored and transported as an aqueous solution is about 62% by weight. Its limit of solubility is only slightly higher than this. As it is the glyphosate rather than the IPA component that is active as a herbicide, concentrations are most usefully expressed in terms of glyphosate acid equivalent (a.e.). A 62% by weight glyphosate IPA salt solution contains about 46% glyphosate a.e. by weight. Even at this concentration, problems can occur, including crystallization of glyphosate salt when stored for prolonged periods of time at low temperatures, and difficulties in pouring and/or pumping as a result of the high viscosity of the solution, especially at low temperatures.
Few salts of glyphosate are soluble enough in water to permit convenient storage and shipping at concentrations significantly higher than 62% by weight. The TMS salt is highly soluble and is useful in some situations, but cannot substitute for the IPA salt in all applications.
It might be thought that by selecting a counterion for glyphosate, such as ammonium ion, having significantly lower molecular weight than IPA, higher glyphosate a.e. concentrations would be possible. For example, at a salt concentration of 36% by weight, a glyphosate ammonium salt solution contains about 33% a.e. by weight, whereas a glyphosate IPA salt solution contains only about 27% a.e. by weight. Unfortunately, the solubility of glyphosate ammonium salt in water is much lower than that of the IPA salt, thus this apparent advantage cannot be exploited in highly concentrated solutions, for example of 40% a.e. by weight or higher.
An approach that has found utility has been to prepare the glyphosate as a dry salt. Many glyphosate salts, including the IPA and TMS salts, are difficult and expensive to prepare in a dry form, but the ammonium and sodium salts are more amenable to this approach. For example, a dry water-soluble powder or granular formulation of glyphosate ammonium salt containing about 95% by weight of that salt can be manufactured on a commercial scale; such a formulation has a glyphosate a.e. content of about 86% by weight. This would appear at first sight to provide an excellent solution to the problem of packing more glyphosate a.e. into a container of given capacity. Unfortunately, however, the bulk density of such a powder or granular formulation is rather low, so that the benefit is not as great as might be thought. Also, many end-users and many distributors prefer a liquid product because of flexibility in handling, thus the need remains for a more compact storage and shipping system for a glyphosate salt in liquid form.
Among the water-soluble salts of glyphosate known in the literature, but never used commercially, are the potassium salt and the monoethanolammonium (MEA) salt. These salts are disclosed, for example, by Franz in U.S. Pat. No. 4,405,531 cited above, among a very long list of salts of glyphosate useful as herbicides.
Few herbicides have been commercialized as their potassium or MEA salts. The Pesticide Manual, 11th Edition, 1997 lists as potassium salts the auxin type herbicides 2,4-DB ((2,4-dichlorophenoxy)butanoic acid), dicamba (3,6-dichloro-2-methoxybenzoic acid), dichlorprop (2-(2,4-dichlorophenoxy)propanoic acid) and MCPA ((4-chloro-2-methylphenoxy)acetic acid), and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), the active ingredient of certain herbicide products sold by DowElanco under the trademark Tordon(copyright). Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is formulated as its MEA salt in certain herbicide products sold by DowElanco under the trademark Lontrel(copyright).
Glyphosate potassium salt has a molecular weight of 208. Glyphosate MEA salt has a molecular weight of 230, very similar to that of glyphosate IPA salt (228).
Solubility in water of the potassium and MEA salts of glyphosate is believed not to be recorded in prior art but is readily determined by procedures familiar to those skilled in the art. Similarly, aqueous solutions of these salts at concentrations greater than about 40% by weight are believed not to have been specifically disclosed, thus any unusual or unpredicted properties of such solutions have not been publicly known. Concentrations expressed as percent by weight herein relate to parts by weight of salt or acid equivalent per 100 parts by weight of solution.
It can now be disclosed that glyphosate potassium salt has been determined to have a solubility in pure water at 20xc2x0 C. of about 54% by weight, that is, about 44% glyphosate acid equivalent (a.e.) by weight. It can further be disclosed that glyphosate MEA salt has been determined to have a solubility in pure water at 20xc2x0 C. of about 64% by weight of solution, that is, about 47% glyphosate a.e. by weight. The solubility of the MEA salt is very similar to the solubility of the IPA salt. Thus a simple aqueous solution concentrate of glyphosate MEA salt can readily be provided at a concentration of, for example, 46% a.e. by weight, comparable to that commercially obtainable with glyphosate IPA salt, as in the aqueous solution concentrate available from Monsanto Company under the name MON 0139.
While it would be desirable, as indicated above, to have a compact storage and shipping system for glyphosate salt, it would also be desirable to have a compact storage and shipping system for glyphosate salt accompanied by one or more surfactants in an agronomically useful amount.
An xe2x80x9cagronomically useful amountxe2x80x9d means a sufficient amount of the surfactant or surfactants to provide a benefit in terms of improved herbicidal effectiveness by comparison with the glyphosate salt applied in the absence of surfactant. It would be especially desirable to have a compact storage and shipping system for glyphosate salt accompanied by one or more surfactants in an amount sufficient to provide herbicidal effectiveness on one or more important weed species at least equal to that of current commercial glyphosate IPA salt products such as Roundup(copyright) herbicide, without the need for further surfactant to be added by the user.
The glyphosate composition forming part of a compact storage and shipping system must be storage-stable. By xe2x80x9cstorage-stablexe2x80x9d, in the context of a concentrated aqueous solution of glyphosate salt, is meant not forming crystals of glyphosate or salt thereof on exposure to a temperature not lower than about 0xc2x0 C. for a period of up to about 7 days. Ideally the composition should withstand temperatures not lower than about xe2x88x9210xc2x0 C. for up to about 7 days without crystal formation, even in the presence of seed crystals of the glyphosate salt. Where the glyphosate composition also contains a surfactant, storage-stability requires, at a minimum, that the composition does not exhibit phase separation at temperatures of about 50xc2x0 C. or lower, ideally at temperatures of about 60xc2x0 C. or lower. Preferably such a surfactant-containing composition should also withstand temperatures not lower than about 0xc2x0 C. for up to about 7 days without crystal formation.
A surfactant that is described herein as xe2x80x9ccompatiblexe2x80x9d with a glyphosate salt at specified surfactant and glyphosate a.e. concentrations is one that provides a storage-stable composition as defined immediately above containing that surfactant and salt at the specified concentrations.
Users of liquid herbicidal products typically meter the dosage by volume rather than by weight, and such products are usually labeled with directions for suitable use rates expressed in volume per unit area, e.g., liters per hectare (l/ha) or fluid ounces per acre (oz/acre). Thus the concentration of herbicidal active ingredient that matters to the user is not percent by weight, but weight per unit volume, e.g., grams per liter (g/l) or pounds per gallon (lb/gal). In the case of glyphosate salts, concentration is often expressed as grams of acid equivalent per liter (g a.e./l).
Historically, surfactant-containing glyphosate IPA salt products such as Roundup(copyright) and Roundup(copyright) Ultra herbicides of Monsanto Company have most commonly been formulated at a glyphosate concentration of about 360 g a.e./l. The surfactant-containing glyphosate TMS salt product Touchdown(copyright) of Zeneca has been formulated at a glyphosate concentration of about 330 g a.e./l. Products at lower a.e. concentration, i.e., more dilute, are also sold in some markets, but carry a cost penalty per unit of glyphosate they contain, primarily reflecting packaging, shipping and warehousing costs.
Further benefits in cost saving and in convenience to the user are possible if the concentrated aqueous solution of glyphosate salt forming part of a compact storage and shipping system and having an agronomically useful amount of surfactant can be provided at a glyphosate concentration significantly higher than 360 g a.e./l, for example about 420 g a.e./l or higher, or even about 480 g a.e./l or higher. It would be especially beneficial if such a compact storage and shipping system could further permit easy pouring and/or pumping of the concentrated solution, even at low temperatures.